1. Field of the Invention
The invention relates to a metering device and method for delivering fluid that utilizes a compensating element.
2. Description of the Prior Art
Traditional metering devices include a fluid chamber that is situated in a housing wherein the fluid chamber contains a pressurized fluid that is discharged through an orifice or opening of the metering device and into an outside space. The traditional metering devices further include a valve needle that can be displaced by an actuating drive such that movement of the valve needle opens and closes the opening of the metering device.
The metering process typically occurs at high speed such that the actuating drive and the valve needle move a distance that ranges from 30 xcexcm to 40 xcexcm. Likewise, the metering device components, such as the actuating drive and valve needle, shift or move due to external factors, such as varying temperature loads, aging effects, and settling effects. This shifting or movement is of the same order of magnitude as the movement of the metering components, such as the valve needle and actuating drive, during the metering process as previously discussed. This shifting or movement due to varying thermal loads typically occurs within an injector of an automobile engine. The varying thermal load typically ranges from xe2x88x9240xc2x0 C. to 160xc2x0 C.
However, the shifting or movement of the metering device due to external factors can cause the metering device to operate less effectively. For example, the opening of the metering device may not remain hydraulically sealed due to the shifting or movement because the components can move or shift at different rates or Wearying positions relative to each other. Aging and settling can result in similar effects on the metering device.
To compensate for this shifting or movement due to varying temperature loads, attempts have been made to thermally balance the metering device by appropriately selecting thermally compatible materials for each of the individual metering device components. However, a device or method that utilizes this compensation technique is not known for varying temperature loads that range from xe2x88x9240xc2x0 C. to 160xc2x0 C.
The German Patent Application P 19838862.4 discloses a metering device wherein the actuating drive controls the movement of a valve needle via a hydraulic chamber. The hydraulic chamber is connected to a hydraulic storage that is positioned in the fluid chamber and also serves as a pressure reserve. The connection between the hydraulic chamber and the hydraulic storage is made in a throttled manner so that the fast movement of the actuating drive is hydraulically transferred to the valve needle, whereas a slow change of pressure in the hydraulic chamber due to a varying thermal load, for example, can be compensated by a fluid compensation with the hydraulic storage.
An objective of the present invention is to provide a metering device and method for delivering fluid that compensates for shifting or movement of various metering device components due to varying thermal loads or other external factors, such as aging or settling effects.
A further objective of the present invention is to provide a simplified, reliable and precise metering device and method of delivering fluids that compensates for the shifting or movement of various metering device components due to varying thermal loads or other external factors.
The present invention includes a valve needle that is positioned within a fluid chamber. The valve needle is attached to a compensating element. The compensating elements operates to compensate for the shifting or movement of the valve needle or other metering device components due to varying thermal loads or other external factors while at the same time resulting in negligible, if any, lift loss as the valve needle moves to delivery fluid during the metering process.
The valve needle further includes a first needle part that is connected to the actuating drive and a second needle part by which the orifice or opening of the metering device can be closed or opened. In addition, the compensating element includes a compensating element hydraulic chamber that is defined by a first wall, a second wall and an outside wall wherein the first wall, second wall and outside wall are flexibly interconnected. The compensating element hydraulic chamber is connected to the metering device fluid chamber by a compensating element opening. This opening is constructed such that the change of pressure of the fluid in the compensating element hydraulic chamber due to the fluid exchange between the compensating element hydraulic chamber and the fluid chamber does not significantly influence the transfer of movement from the first needle part to the second needle part of the valve needle during the delivery of fluid of the metering process.
On the other hand, this opening is constructed such that the shifting or movement of the valve needle or other metering device component due to varying thermal loads or other external factors is balanced or compensated by balancing the pressures of the compensating element hydraulic chamber and the metering device fluid chamber. Typically, the shifting or movement due to external factors, such as varying thermal loads, is on order of magnitude 100 to 1000 times slower as compared to the movement of the valve needle or other metering device components during the delivery of fluid of the metering process. Because of the relatively slow shifting or movement of the valve needle due to varying thermal loads or other external factors, a change of pressure in the hydraulic chamber is balanced by a fluid exchange with the fluid chamber such that the movement of one needle part is not transferred to the respective other needle part. For example, the compensating element hydraulic chamber compensates for a slow displacement of the valve needle relative to the housing due to varying thermal loads or other factors by changing its volume without effecting a pressure buildup in the hydraulic chamber of the housing of the metering device.
Therefore, a change in the length or shifting or movement of various components of the metering device, such as the valve needle, due to varying temperature loads or other factors, is balanced by a modified spacing between the first wall and the second wall of the compensating element. In an initial position, this spacing is adjusted by the balance between the inertial force acting on the valve needle in an axial direction and the spring force of the connecting compensating element outside wall.
In an embodiment, the present invention provides that the first and second wall of the compensating element are fastened perpendicularly and centered relative to the longitudinal axis of the valve needle.
In a further embodiment, the first and second wall of the compensating element are discoid or disk-shaped and have the same diameter.
In an embodiment, the compensating element can be inserted independently of the shape of the first wall and the second wall wherein the mass of the first and second walls is advantageously minimal in order to avoid inertial effects during the respective fluid delivery operation. The first and second walls can also be radially offset to one another and likewise can be tilted with respect to the longitudinal axis of the valve needle.
In an embodiment, the outside wall of the compensating element includes metal bellows wherein the metal bellows are stainless steel due to the high corrosive resistance property and durable and lasting wear of stainless steel. The outside wall is preferably attached to the outside of the contact area of the first and second wall of the compensating element so that damage to the outside wall can be avoided as a result of the contact made between the first and second walls
In an embodiment, the compensating element hydraulic chamber exhibits a high spring constant so that lift loss does not occur due to the elasticity of the enclosed fluid volume. The high spring constant can be preferably achieved by a low height of the compensating element chamber.
In an embodiment, the metering device with the compensating element of the present invention is utilized for fuel injection, preferably gasoline direct injection.
In an embodiment, the valve needle opens to the outside of the metering device.
In an embodiment, the valve needle opens to the inside of the metering device.
An advantage of the present invention is that it provides a simple construction in contrast to traditional metering devices.
Another advantage of the present invention is that the compensating element operates to adjust or compensate for shifting or movement of a variety of metering device components, including the valve needle and housing, due to external factors, such as varying thermal loads, aging or settling effects.
It is still yet another advantage of the present invention to compensate for the shifting and movement of various metering device components due to external factors resulting in negligible, if any, lift loss of the valve needle during the delivery of fluid of the metering process.